In LCD, for example, it is indispensable to dispose polarizers on both sides of a glass substrate providing a surface of a liquid crystal panel according to an image formation scheme adopted in the display. A polarizer is generally obtained in a procedure in which a polyvinyl alcohol-based film is dyed with a dichroic material such as iodine, thereafter, the film is crosslinked with a crosslinking agent and then, mono-axially stretched to thereby form a film. Since the polarizer is manufactured by stretching, it is easy to shrink. Since a polyvinyl alcohol-based film comprises a hydrophilic polymer, the film is very easily deformed especially in a humidified condition. Since the film itself is weak in mechanical strength, there has been a problem that the film is torn. Hence, adopted is a reinforced polarizing plate manufactured in a procedure in which a transparent protective film or transparent protective films each made from triacetyl cellulose or the like are adhered to on one side or both sides of a polarizer. The polarizing plate is manufactured by adhere the transparent protective film onto a polarizer using an adhesive. As an adhesive for polarizing plates used in adhesion of the polarizer and the transparent protective film to each other, an aqueous type adhesive is conventionally preferable and, for example, a polyvinyl alcohol-based adhesive obtained by mixing a crosslinking agent into a polyvinyl alcohol aqueous solution has been employed.
In recent years, improvement on image uniformity and a quality thereof has been requested in company with progress toward higher definition and higher functionality of LCD. Further, durability such as high temperature resistance, moisture resistance or water resistance has also been requested in order to cope with diversification of a use environment. Decrease in thickness and reduction in weight have also been requested due to such as portability of LCD in recent years. Such required characteristics of LCD has rendered another requests imposed on higher performance and a higher functionality, such as uniformity, moisture resistance, heat resistance and decrease in thickness, of a polarizing plate for LCD.
A polyvinyl alcohol-based adhesive is insufficient in moisture and heat resistance and water resistance, and a case of peeling arises at the interface between a polarizer and a transparent protective film in a humidified environment. This is considered because a polyvinyl alcohol-based resin, which is a main component of the adhesive, is a water-soluble polymer and a possibility of dissolution of an adhesive occurs in a situation of dewing.
In order to cope with the problem, a proposal has been offered of an adhesive for polarizing plates containing a polyvinyl alcohol-based resin having an acetoacetyl group, and a crosslinking agent (see, for example, Japanese Unexamined Patent Publication No. 7-198945:Patent Literature 1). An adhesive for polarizing plates described in Patent Literature 1 makes improvement on durability such as moisture resistance and heat resistance and water resistance. However, the adhesive for polarizing plates described in Patent Literature 1 does not show a sufficient pot life. That is, since a pot life and durability of an adhesive have a relationship of a trade-off therebetween, an adhesive laying emphasis on a pot life but insufficient in durability has been used in manufacturing a conventional polarizing plate in consideration of productivity.